Vibert N, Serafin M, Vidal P P, Mühlethaler M
Département de Physiologie, CMU, Geneva, Switzerland.
Exp Brain Res. 1995;104(2):351-6. doi: 10.1007/BF00242021.
Inhibitory amino acids are considered as major transmitters in the vestibular system. Using intracellular recordings in slices, we applied gamma-aminobutyric acid (GABA) and muscimol (a specific agonist of the GABAA receptor) to the two main types of medial vestibular nucleus neurones (A and B MVNn). In either a high Mg2+/low Ca2+ solution, or a solution containing tetrodotoxin, all MVNn were hyperpolarized by GABA and muscimol. This indicates that both types of MVNn are endowed with postsynaptic, hyperpolarising GABAA receptors. In a normal medium, about half of A and B MVNn were, in contrast, depolarised by GABA and muscimol, whereas the remaining cells were hyperpolarised. These results could be due to a modulation by GABA and muscimol of a tonic GABA release in the slice. Such a release was, indeed, suggested by results showing the depolarising effect of either tetrodotoxin (TTX) or bicuculline, when applied alone. The cells that were depolarised by GABA or muscimol in control conditions were always hyperpolarised in the presence of TTX. Our data therefore suggest that GABA acting at GABAA receptors in the medial vestibular nucleus can play a role either through a postsynaptic hyperpolarising action or indirectly by inhibiting a tonic GABA release, probably resulting from the spontaneous activity of local inhibitory interneurones. A GABAergic regulation of these interneurones could be important in processes of vestibular habituation and/or adaptation.
抑制性氨基酸被认为是前庭系统中的主要神经递质。我们利用脑片细胞内记录技术，将γ-氨基丁酸（GABA）和蝇蕈醇（GABAA受体的特异性激动剂）施加于内侧前庭核神经元的两种主要类型（A和B型内侧前庭核神经元）。在高镁离子/低钙离子溶液或含有河豚毒素的溶液中，所有内侧前庭核神经元均被GABA和蝇蕈醇超极化。这表明两种类型的内侧前庭核神经元都具有突触后超极化的GABAA受体。相比之下，在正常培养基中，约一半的A型和B型内侧前庭核神经元被GABA和蝇蕈醇去极化，而其余细胞则被超极化。这些结果可能是由于GABA和蝇蕈醇对脑片中持续性GABA释放的调节作用。单独应用河豚毒素（TTX）或荷包牡丹碱时所产生的去极化效应的结果确实提示了这种释放。在对照条件下被GABA或蝇蕈醇去极化的细胞在TTX存在时总是被超极化。因此，我们的数据表明，作用于内侧前庭核中GABAA受体的GABA可以通过突触后超极化作用发挥作用，或者通过抑制可能由局部抑制性中间神经元的自发活动导致的持续性GABA释放而间接发挥作用。这些中间神经元的GABA能调节在前庭习惯化和/或适应过程中可能很重要。
